The present invention relates to a method of differentiating between persons and other objects on vehicle seats by sensing and evaluating the pressure distribution caused by them on the seat. In particular, this method is used to differentiate whether a seat is occupied by a person or a child seat in order to, for example, prevent activation of an air bag if the seat is occupied by a child seat, in contrast to being occupied by a person.
The occupants of a motor vehicle are normally protected from the effects of a collision of the vehicle by restraining systems, among others, for example, by one or more air bags. In this case, a differentiation has to be made as to whether a seat is occupied by a child seat or by a person. In the case of a child seat, the air bag should not be triggered because of the possible lethal effect on the child, particularly if the child seat is oriented against the driving direction. In the case of a person, the air bag should be triggered in order to protect the person.
Furthermore, it is desirable to receive additional information concerning the type of seat occupation from the participating sensor system in order to be able to react in a flexible manner. Thus, there are endeavors, for example, to inflate an air bag to an extent which varies with the type of accident or with the crash intensity; to also use side air bags in a supplementary manner, if required; to activate belt tightening devices at a different intensities depending on the requirement, etc. If it is determined that the seat is occupied by an adult person, it is additionally desirable to precisely know the person's sitting position and react to it in a flexible manner. Sitting positions also exist for adults in which the inflation of an air bag is not recommended under certain circumstances because there is the risk of great harm to the health of the passenger.
For economical reasons, all attempts to solve these problems additionally have to achieve cost effectiveness in order for the method used to be applicable in series production. The sensor system used should be producible in a cost-effective manner and should be capable of being integrated in the vehicle and be serviced at acceptable expenditures.
Among others, camera systems, optical sensors and ultrasonic sensors can be used as sensor systems, as well as pressure sensors in the vehicle seats. Although camera systems can supply very extensive information concerning the events in the vehicle occupant compartment, they are expensive in series production and may also require extensive maintenance. In addition, attention should be paid to shading in the case of all sensors operating with light or ultrasound. Pressures sensors in the vehicle seats can be produced in a cost-effective manner, are robust, require low-maintenance and are not affected by the shading problem.
The first attempts were limited to a determination of the total weight by means of pressure sensors. This solution is unsatisfactory because, in the case of an adult person, a portion of his/her weight is taken-up by the backrest as well as by the floor via one's feet which are, as a rule, placed on the vehicle floor. Measuring using sensors integrated in the vehicle seat will, therefore, always only supply a lower limit of the occupant's total weight. It should also be considered here that child seats are placed in the vehicle with a pretensioned belt and therefore may load the seat by a force which is clearly higher than their own weight. The limits between a low-weight adult and a heavy child seat can, therefore, easily become blurred if only the total weight is used as a criterion.
For example, in Luxembourg Patent document LU 90106 and U.S. Pat. No. 6,348,663, the pressure pattern of a seated person is analyzed in such a manner that the seat surface is divided into several sectors and the weight distribution onto these sectors is determined and analyzed. A conclusion is drawn therefrom concerning the person's height or the person's weight or concerning both. Both constructions contain no criteria which differentiate persons from other objects.
U.S. Pat. No. 6,243,634 discloses sensors in the entire seat, thus also in the backrest, in order to achieve an improved determination of the weight, of the center of gravity and of the position. As a result, an improved detection of non-optimal seat positions is endeavored, for example, whether a person is bending forward. However, this document does not relate to a differentiation between persons and other objects, no criterion being given for this purpose.
U.S. Pat. Nos. 5,941,560 and 6,170,866 explicitly mention the protection of children in child seats in their title. A prerequisite in both documents is the existence of a sensor system, which is not described in detail and which is capable of detecting child seats. As a reaction, either a signal is emitted for informing the driver, or the vehicle seat is automatically moved toward the rear. No analysis of the pressure pattern is carried out here.
In U.S. Pat. No. 6,366,200, a differentiation is made between an occupation of the vehicle seat by a child, an adult or a child seat. The criteria are, on the one hand, the weight and, on the other hand, the signal of a sensor which is described by the term “living body proximity sensor”; that is, a sensor which indicates the proximity of a living object.
In U.S. Pat. No. 6,272,411, the signals of several sensors are combined in order to obtain information which is as complete as possible concerning the status of the seat occupation. It is to be determined whether the seat is vacant or occupied, and if it is occupied, how it is occupied. The invention significantly stresses the analysis of dynamic information; that is, sensor signals are detected as a function of time and are periodically compared with a databank in order to be able to derive additional information from the time response. On the basis of this information, a decision is made not only concerning the use or non-use of the air bag, but also concerning the control of the inflation intensity, concerning side air bags, etc.
U.S. Pat. No. 6,252,240 operates with a combination of several sensors, among others, position-sensitive optical sensors, weight sensors and speed sensors. Probabilities are computed for defined scenarios, and the air bag is controlled corresponding to the most probable scenario. In this case, no analysis of pressure patterns is used for differentiating between persons and other objects.
It is an object of the present invention to provide a method of detecting a pattern on vehicle seats, which method reliably differentiates between persons and other objects, particularly child seats. The methods should also be simple from a constructional point of view and avoid the above-mentioned disadvantages of the prior art.
According to the invention, this object is achieved by providing a method of differentiating between persons and other objects on vehicle seats by sensing and evaluating the pressure distribution caused by them on the seat, wherein a mean deviation of the signal at one position from the mean signal of its neighborhood differs between persons and other objects.
A first embodiment of the invention (criterion of local flatness) evaluates statistically how much the pressure signal at one position differs from its neighborhood.
The essential advantages achievable by means of the invention consist of the fact that only few criteria are required, and the criteria are not dependent on special sensor structures (matrix-like, discrete, etc.). In addition, to the extent that it is required, only a simple logical linking of the individual criteria has to be carried out. Other methods according to the prior art have to combine the individual criteria with high-expenditure algorithms.
A neighborhood in the sense of the invention consists of the fact that neighboring positions belong to a common cohesive area. Mathematically, an area is cohesive if two arbitrary points of the area can be connected by a connection path which extends completely within the area, and thus never leaves the area.
The advantages of this further development essentially consist of the fact that it is a statistical method which is independent of the shape of the object situated on the seat or of the person situated on the seat.
Another embodiment of the invention excludes a person when defined constellations of areas occur which are more characteristic of technical objects than of persons. In particular, in the case of a matrix-shaped sensor arrangement, a technical object, thus, for example, a child seat, can easily generate a pressure pattern in which an entire column of sensors supplies no signal. There are child seats which have two runners on their underbody which extend in the driving direction. Their pressure pattern may easily have one or more columns in which not a single sensor supplies a signal. Such an arrangement virtually does not occur in the case of a person.
A further embodiment according to the invention excludes a person if no signal, or only a very slight signal, is present in a certain area. For example, in the case of matrix-shaped sensor arrangements, child seats frequently have few or even no sensor signals at all in an area in the interior of the seat pattern.
The advantages of the further developments according to the invention consist essentially of the fact that these further developments are based on no absolute pressure value. In the case of a discrete pressure distribution, they are not sensitive to a special calibration curve of the pressure sensors, but only possibly to the position of their activation points. In addition, they are, as a rule, successful in simple constellations.
The methods will be described in the following by means of preferred embodiments as examples. For this purpose, reference is made to the drawings, in which the same reference numbers in each case refer to identical details.